When comparing the stats of the two creatures for Evolving Adaptive's last ability, you always compare power to power and toughness to toughness.

Whenever another creature enters the battlefield under your control, check its power and toughness against the power and toughness of Evolving Adaptive. If neither stat of the new creature is greater, the last ability won't trigger at all.

If the ability triggers, the stat comparison will happen again when the ability tries to resolve. If neither stat of the new creature is greater, the ability will do nothing. If the creature that entered the battlefield leaves the battlefield before the ability tries to resolve, use its last known power and toughness to compare the stats.

If a creature enters the battlefield with +1/+1 counters on it, consider those counters when determining if Evolving Adaptive's ability will trigger.

When comparing the stats as the ability resolves, it's possible that the stat that's greater changes from power to toughness or vice versa. If this happens, the ability will still resolve and you'll put an oil counter on Evolving Adaptive. For example, if you control an Evolving Adaptive with two oil counters and a 1/3 creature enters the battlefield under your control, its toughness is greater so the ability will trigger. In response, the 1/3 creature gets +2/-2. When the ability tries to resolve, its power is greater. You'll put an oil counter on Evolving Adaptive.

If multiple creatures enter the battlefield at the same time, Evolving Adaptive's ability may trigger multiple times, although the stat comparison will take place each time one of those abilities tries to resolve. For example, if you control an Evolving Adaptive with two oil counters on it and two 3/3 creatures enter the battlefield, the ability will trigger twice. The first ability will resolve and put an oil counter on Evolving Adaptive. When the second ability tries to resolve, neither the power nor the toughness of the new creature is greater than that of Evolving Adaptive, so that ability does nothing.